docs(resources): ngrx-entity-relationship

[satanTime]

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/ngrx/platform/blob/master/CONTRIBUTING.md#commit
• Tests for the changes have been added (for bug fixes / features)
• Documentation has been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

[ ] Bugfix
[ ] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] CI related changes
[x] Documentation content changes
[ ] Other... Please describe:

What is the current behavior?

no info about the lib https://github.com/satanTime/ngrx-entity-relationship

What is the new behavior?

a section with the info about the lib https://github.com/satanTime/ngrx-entity-relationship

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information

Hi guys, thanks for NGRX, it's awesome.

There is the known problem about selecting relational data. I always tried to approach it in different ways, and, looks like, finally, I found a solution that might work not only for me, but also for other devs.
Also, when I read this section in the docs, I feel a bit upset, and I hope that one day it will be removed.

Unfortunately, I'm not familiar with standards for being listed in the official docs. Therefore, feel free to point me to any issues I should solve for that.

Thank you in advance and happy coding!

[ngrxbot]

Preview docs changes for 2ac8eb3 at https://previews.ngrx.io/pr2866-2ac8eb32/

[satanTime]

Cool, thanks!